How to Make It
Stir together all ingredients a small bowl. Let stand at room temperature 1 hour.
While finadene stands, grind barley to a fine powder in a spice grinder. Heat a nonstick skillet over medium-high; add barley, and cook, tossing constantly, until golden brown and toasted, about 5 minutes. Remove from heat; let cool in skillet 2 minutes. Return skillet to medium-high; whisk in mirin and sake until smooth. Add soy sauce, brown sugar, sherry vinegar, garlic, scallions, ginger, and peppercorns; cook, stirring often, 15 minutes. Pour mixture through a fine wire-mesh strainer into a bowl; discard solids. Set sauce aside for basting.
Sprinkle steak pieces with salt and pepper. Thread steak pieces onto 8 (12-inch) skewers. Brush with basting sauce; let stand at room temperature while grill preheats.
Open bottom vent of a charcoal grill completely. Light charcoal chimney starter filled with briquettes. When briquettes are covered with gray ash, pour onto bottom grate of grill. Adjust vents as needed to maintain an internal temperature of 550°F to 600°F. (If using a gas grill, preheat to very high [500°F and up].) Place skewers on oiled grates. Grill, uncovered, flipping and basting with sauce until steak pieces are charred in some spots and a meat thermometer registers 125°F, about 8 to 10 minutes for medium-rare.
Transfer skewers to a cutting board, and let steak rest 5 to 10 minutes. Serve with finadene.